Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, one or more magnetic disks 16, supported for rotation by a drive spindle 18 of motor 14, and an actuator 20 including at least one arm 22, the actuator being attached to a pivot bearing 24. Suspensions 26 are coupled to the ends of the arms 22, and each suspension supports at its distal end a read/write head or transducer 28. The head (which will be described in greater detail with reference to FIGS. 2A and 2B) typically includes an inductive write element with a sensor read element. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 28 causing it to lift slightly off of the surface of the magnetic disk 16, or, as its is termed in the art, to “fly” above the magnetic disk 16. Alternatively, some transducers, known as contact heads, ride on the disk surface. Various magnetic “tracks” of information can be written to and/or read from the magnetic disk 16 as the actuator 20 causes the transducer 28 to pivot in a short arc across a surface of the disk 16. The pivotal position of the actuator 20 is controlled by a voice coil 30 which passes between a set of magnets (not shown) to be driven by magnetic forces caused by current flowing through the coil 30.
FIG. 2A shows the distal end of the head 28, greatly enlarged so that a write element 32 incorporated into the head can be seen. The write element 32 includes a magnetic yoke 34 having an electrically conductive coil 36 passing therethrough.
The write element 32 can be better understood with reference to FIG. 2B, which shows the write element 32 and an integral read element 38 in cross section. The head 28 includes a substrate 40 above which the read element 38 and the write element 32 are disposed. A common edge of the read and write elements 38, 32, defines an air bearing surface ABS, in a plane 42, which can be aligned to face the surface of the magnetic disk 16 (see FIGS. 1A and 1B). The read element 38 includes a first shield 44, a second shield 46, and a read sensor 48 that is located within a dielectric medium 50 between the first shield 44 and the second shield 46. The most common type of read sensor 48 used in the read/write head 28 is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic field being sensed.
The write element 32 can be better understood with reference to FIG. 2B, which shows the write element 32 and an integral read element 38 in cross section. The head 28 includes a substrate 40 above which the read element 38 and the write element 32 are disposed. A common edge of the read and write elements 38, 32, defines an air bearing surface ABS, in a plane 42, which can be aligned to face the surface of the magnetic disk 16 (see FIGS. 1A and 1B). The read element 38 includes a first shield 44, a second shield 46, and a read sensor 48 that is located within a dielectric medium 50 between the first shield 44 and the second shield 46. The most common type of read sensor 48 used in the read/write head 28 is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic field being sensed.
The write element 32 is typically an inductive write element that includes the second shield 46 (which functions as a first pole for the write element) and a second pole 52 disposed above the first pole 46. Since the present invention focuses on the write element 32, the second shield/first pole 46 will hereafter be referred to as the “first pole”. The first pole 46 and the second pole 52 contact one another at a backgap portion 54, with these three elements collectively forming the yoke 34. The combination of a first pole tip portion and a second pole tip portion near the ABS are sometimes referred to as the ABS end 56 of the write element 32. Some write elements have included a pedestal 55 which can be used to help define track width and throat height. A write gap 58 is formed between the first and second poles 46 and 52 in the area opposite the back gap portion 54. The write gap 58 is filled with a non-magnetic, electrically insulating material that forms a write gap material layer 60. This non-magnetic material can be either integral with or separate from a first insulation layer 62 that lies upon the first pole 46 and extends from the ABS end 56 to the backgap portion 54. The conductive coil 36, shown in cross section, passes through the yoke 34, sitting upon the write gap material 60. A second insulation layer 64 covers the coil and electrically insulates it from the second pole 52.
An inductive write head such as that shown in FIGS. 2A and 2B operates by passing a writing current through the conductive coil 36. Because of the magnetic properties of the yoke 28, a magnetic flux is induced in the first and second poles 46 and 52 by write currents passed through the coil 36. The write gap 58 allows the magnetic flux to fringe out from the yoke 34 (thus forming a fringing gap field) and to cross the magnetic recording medium that is placed near the ABS.
With reference to FIG. 2C, a critical parameter of a magnetic write element is the trackwidth of the write element, which defines track density. For example, a narrower trackwidth can result in a higher magnetic recording density. The trackwidth is defined by the geometries in the ABS end 56 of the yoke. For example, the track width can be defined by the width W3 of the pedestal 55 or by the width W1 of the second pole 52, depending upon which is smaller. The widths W3 and W1 can be the same, such as when the second pole 52 is used to trim the pedestal 55. Alternatively, in designs that have no pedestal at all it would be possible to define the trackwidth by the width W2 of the first pole.
With reference to FIG. 2B, the fringing gap field of the write element can be further affected by the positioning of the zero throat level ZT. ZT is defined as the distance from the ABS to the first divergence between the first and second pole, and it can be defined by either the first or second pole 46, 52 depending upon which has the shorter pole tip portion. Pedestal defined zero throat is defined by the back edge of the pedestal and is accomplished by moving the second insulation layer 64 back away from the ABS. Alternatively, zero throat can be defined by the geometry of the second pole 52, by allowing the second insulation layer 64 to extend over the top of the pedestal. In order to prevent flux leakage from the second pole 52 into the back portions of the first pole 46, it is desirable to provide a zero throat level that is well defined with respect to the plane of the ABS. Furthermore, a pedestal defined zero throat is beneficially defined along a well defined plane that is parallel with the plane 42 of the ABS, whereas a zero throat defined by the second pole occurs along the sloped edge of the second insulation layer 64. As will be appreciated upon a reading of the description of the invention, the present invention can be used with either pedestal defined zero throat or a second pole defined zero throat. Thus, accurate definition of the trackwidth, and zero throat is critical during the fabrication of the write element.
The performance of the write element is further dependent upon the properties of the magnetic materials used in fabricating the poles of the write element. In order to achieve greater overwrite performance, magnetic materials having a high saturation magnetic flux density (high Bsat) are preferred. A common material employed in forming the poles is high Fe content (55% Fe) NiFe alloy having a Bsat of about 16 kG. However, high Fe content NiFe alloy has a high magnetostriction constant λs (on the order of 10−5) which causes undesirable domain formation in the poles. It is known that the domain wall motion in the writer is directly related to the increase in popcorn noise in the read element, especially when the motion occurs in the first pole, which also serves as a shield for the read element. A reduction in popcorn noise in the read element can be achieved through the use of soft magnetic materials, (i.e. materials having a low magnetostriction constant) in the fabrication of the first pole 46. However, such materials generally have limited Bsat.
Therefore, there remains a need for a write element having the ability to concentrate a high degree of magnetic flux in the ABS end of the write element, while minimizing or eliminating popcorn noise caused by magnetostrictive properties of the write element. Such a write element would preferably provide a narrow and accurately controlled trackwidth as well as providing high overwrite, low non-linear transition shift, a high areal density and high data rate.